Term
|
Definition
A layered group of three membranes that surround the entire CNS
Pachymeninx - "thick membrane"
- Dura Mater
Leptomeninges - "thin membrane"
- Arachnoid
- Pia mater |
|
|
Term
|
Definition
-thick membrane
-A strong, fibrous membrane that forms the most superficial layer of meningnes
-Covers the nerve roots. Fuses with the vertebral periosteum & the epineureum at the intervertebral foramina
-Lines the vertebral canal to the level of about S2
-Filum terminale externum: Terminal strand continuation of dura down to a final attachment in the coccyx |
|
|
Term
|
Definition
It is a Leptomeninge - "thin membrane"
A delicate membrane that forms the middle layer of meninges
Lines the deep aspect of the dura throughout its extent
Arachnoid trabeculae: Network of arachnoid fibers that connect the arachnoid & pia mater |
|
|
Term
|
Definition
leptomeninge - thin membrane
Delicate membrane that forms the deep layer of meninges
Lines the exterior surface of the CNS & spinal nerve rootlets & roots. Fuses with the epineureum at the intervertebral formina
Dentate (=denticulate) ligaments: Lateral tooth-like extensions of pia that attach to the dura between the segmental nerve roots. Holds the spinal cord in position within the subarachnoid space.
Filum terminale internum: Terminal strand continuation of pia beyond the conus medullaris. Forms the core of the cauda equine. Finally fuses with the filum terminale externum. |
|
|
Term
| What are the meningeal spaces? |
|
Definition
Epidural (=extradural) space: space surrounding the spinal cord. It is external to dura mater. This is a potential space intracranially
Subdural Space: space between arachnoid & dura. Extends to S2 & contains fluid to moisten the two membranes - existence being questioned
Subarachnoid space: As much as several millimeters wide, surrounding the entire CNS |
|
|
Term
| Explain the epidural space |
|
Definition
Epidural (=extradural) space: space surrounding the spinal cord. It is external to dura mater. This is a potential space intracranially
Contents include
*Epidural fat
*Internal vertebral venous plexus
*Internal vertebral arterial plexus
*Spinal & vertebral nerves
*Lymphatics |
|
|
Term
| Explain the subdural space |
|
Definition
Subdural Space: space between arachnoid & dura. Extends to S2 & contains fluid to moisten the two membranes
Contents include: subdural lymph
Existence being questioned |
|
|
Term
| Explain the subarachnoid space |
|
Definition
Subarachnoid space: As much as several millimeters wide, surrounding the entire CNS
Contents include: cerebospinal fluid (CSF) |
|
|
Term
| Explain caudal (epidural) anesthesia |
|
Definition
| Caudal (epidural) anesthesia is used to block the spinal nerves in the epidural space by injection of local anesthetic. Used for surgery on rectum, anus, genitals, or urinary tract |
|
|
Term
| When does neurulation occur? |
|
Definition
| Neural tube formation (neurulation) occurs during embryonic weeks 3-4 |
|
|
Term
| What is the neural plate? |
|
Definition
| Neural plate: thickened surface ectoderm induced by development of the notochord (neural plate folds to form neural tube) |
|
|
Term
| What is the neural groove? |
|
Definition
| Neural groove: a longitudinal midline depression in the neural plate. It progressively deepens to form the neural canal |
|
|
Term
| What are the neural folds? |
|
Definition
| Neural folds: the elevated lateral edges of the neural plate. Deepening of the neural groove plus growth of the neural plate causes the neural folds to rotate dorsalward around the hinge-like axis of the neural groove. |
|
|
Term
|
Definition
Neural tube: the structure formed by the dorsal midline fusion of the neural folds.
*Will form the brain & spinal cord |
|
|
Term
| What does the neural crest give rise to? |
|
Definition
| Neural Crest will give rise to all of the neurons whose cell bodies are located outside the CNS |
|
|
Term
| What is the central canal? |
|
Definition
| Central canal: the lumen of the neural tube, derived from enclosing the neural groove by the fused neural folds |
|
|
Term
| What are the cranial and caudal neuropores? |
|
Definition
| Cranial and caudal neuropores: Temporary open connections between the central canal and the amniotic cavity at the cranial and caudal ends of the neural tube. |
|
|
Term
| What marks the end of neurulation? |
|
Definition
| Closure of the neurospores produces a closed, tubular CNS characterized by a broader cephalic portion (=brain) and a narrow caudal portion (=spinal cord). |
|
|
Term
| What are the vertebrae and anulus fibrosus of each intervertebral disc derived from? |
|
Definition
|
|
Term
| What produces the neural arch? |
|
Definition
| Dorsal outgrowth derived from the mesenchymal vertebral body |
|
|
Term
| What produces the costal processes |
|
Definition
| Lateral outgrowths derived from the mesenchymal vertebral body |
|
|
Term
| How is the neural arch formed? |
|
Definition
The dorsal outgrowths of each mesenchymal vertebral body grow around the neural tube, between the segmental (=spinal) nerves, and fuse in the midline dorsal to the neural tube, thus forming a complete neural arch
*Neural tube closure induces formation and closure of the neural arch during weeks 3-5 |
|
|
Term
| What is a general overview of spina bifida |
|
Definition
Spina bifida (cleft vertebra)
Linked to low folic acid ingestion during first trimester of prgenancy
The defects most commonly occur at L5 or S1 level
A congenital anomaly characterized by failure of the neural arch elements to fuse with one another in the dorsal midline, resulting in an open vertebral canal
Most common in the sacral and lumbar regions, but may occur elsewhere
The term "spina bifida" covers a wide range of defects
ex - spina bifida occulta and several types of spina bifida cystica |
|
|
Term
| Explain spina bifida occulta |
|
Definition
Spina bifida occulta: Paired neural arch elements have failed to meet in dorsal midline
*Get a tuft of hair or a dimple that forms.
*Neural tube is intact & meninges are around
*Patients are asymptomatic |
|
|
Term
| Explain spina bifida cystica (incl. all 3 types) |
|
Definition
Spina bifida cystica: characterized by fluid filled sac that protrudes
Meningocele: spinal cord remains in place
*Defect in dorsal midline
*Enlarged subarachnoid space
*Dura/arachnoid become incorporated into skin
*May or may not have neurlogic defects depending on pressure
Meningomyelocele: Displacement of spinal cord
*There will be neurologic defects
Myelocele (rachischisis, myeloschisis): Most severe
*Incomplete neural tube
*It is the spinal cord that forms in walls of cyst |
|
|
Term
| What is the positional relationship between the numbered spinal nerves and numbered vertebrae? |
|
Definition
Spinal nerves pass through the corresponding intervertebral foramina
Ex - T2 spinal nerve passes through T2 intervertebral foramina
EXCEPTION!
Cervical mismatch - Because there are 8 cervical nerves and only 7 cervical vertebrae, the C1 nerve passes above C1 vertebrae and the C2 nerve flows through the C1 intevertebral foramina |
|
|
Term
| What is the conus meddularis? |
|
Definition
The tapered, terminal end of the spinal cord
Usu. ends between T12 - L3 |
|
|
Term
| What is the cauda equina? |
|
Definition
A horse's tail-like bundle of nerve roots extending below the conus medullaris
Roots exit at their respective intervertebral formamina |
|
|
Term
| Why does the spinal cord seem to "shrink" over time during development (fetus to adult) |
|
Definition
| The differential growth rates of the spinal cord, vertebral column, and trunk of the body cause the spinal cord to seemingly shrink relative to the vertebral column. |
|
|
Term
| How is the cauda equina formed? |
|
Definition
| Regression of the spinal cord within the vertebral canal causes greater elongation of the lower spinal nerve roots, thus, formation of the cauda equina |
|
|
Term
| How is the large subarachnoid space below the conus meddullaris formed? |
|
Definition
| Regression of the spinal cord within the vertebral canal causes greater separation of the dura-arachnoid from the pia mater below the conus medullaris, thus forming a large subarachonoid space below the conus medullaris |
|
|
Term
| What happens in a herniated disc? |
|
Definition
With herniated disc, get displacement of nucleus pulposus
Along the posterior side is the posterior longitudinal ligament. Nucleus pulposus lays along back of intervertebral disk.
MOST disc herniations will go posterior lateral (around the edges)
Low lumbar & low cervical are common disc herniations |
|
|
Term
| What affect will a cervical herniation have? |
|
Definition
Ex - Posterior lateral disc herniation of C5 will affect C6 spinal nerve
This is because of cervical mismatch |
|
|
Term
| What happens in a lumbar herniation? |
|
Definition
Ex - Posterior lateral herniation of L4 will influence L5 nerve & not the L4
*This occurs because after L3, roots are coming at such a steep angle, they take a tight turn around the pedicles. The roots turn out above the disc at that intervertebral level |
|
|
Term
| Describe the anatomical basis for & clinical significance of a lumbar puncture (spinal tap) |
|
Definition
CSF found in subarachnoid space
Usually done between L4-L5
NOT L3 because the conus medullaris could be there in some people
It also has a nice interlaminar space so you can get the needle through
Any pressure changes in CSF can have significant effects |
|
|
Term
|
Definition
*Whether a spinal nerve enters into plexus formation or retains a simple segmental distribution, each spinal segment/nerve innervates a particular area of skin in a predictable and orderly way
*The area of skin innervated by sensory fibers (ie. by the dorsal root) from a particular spinal segment is termed the DERMATOME for that segment.
There is actually considerable overlap between the territories supplied by nerves arising from adjacent spinal cord segments
Clinical significance
*Cutaneous anesthesia: to obtain total anesthesia of a dermatome, you must influence 3 spinal segments rather than only one |
|
|
Term
| Contrast the dermatome of a spinal nerve with the cutaneous distribution of a peripheral nerve |
|
Definition
DON'T confuse the two - they are different
Most spinal nerves (especially those heading for the limbs) intermingle with one another to form plexuses before arriving at their final destination territories.
Therefore, any one peripheral nerve may have contributions from multiple spinal segments
Therefore:
*The cutaneous territory of any one peripheral nerve may overlap multiple dermatomes
*Any one dermatome may contribute to the cutaneous territories of multiple peripheral nerves |
|
|
